Trinh Thi Ngo, better known to U.S. servicemen as “Hanoi Hannah,” a radio propagandist who delivered daily broadcasts aimed at undermining American morale during the Vietnam War, died Sept. 30 in Ho Chi Minh City.

The Voice of Vietnam, her longtime radio station, announced her death and reported that she was 87. No cause of death was cited.

Ms. Ngo was the most famous of several North Vietnamese broadcasters who served the Communist cause over the radio waves. David Lamb, a respected foreign correspondent who covered the Vietnam War for the Los Angeles Times, once observed that “many considered her Hanoi’s most prominent Communist after Ho Chi Minh,” the revolutionary nationalist leader.

She had perfected her English during her youth in Hanoi, where she was born, studying under a tutor and swooning over American films such as “Gone With the Wind.” Hollywood fare far outdid the European cinema imported to Vietnam during French colonial rule, she found.

“American dialogue was so full of life compared to the boring French films we saw,” she once told an interviewer.

Ms. Ngo in 1995. (Lois Raimondo/AP)

In 1954, after Vietnam gained independence through a guerrilla war waged against the French, the country was divided into the Communist North and the non-Communist South. The United States backed the South with advisers and eventually military forces in the ensuing conflict that became the Vietnam War.

Ms. Ngo, the daughter of what she described as a “nationalist bourgeois family,” soon joined the state-run, northern-based Voice of Vietnam. “I thought it was time for me to do something to contribute to the revolution,” she recalled in an account on her radio station’s website.

Because of her fluency in English, Ms. Ngo became a marquee personality on the Voice of Vietnam as it evolved increasingly into an instrument of propaganda wielded against U.S. forces and prisoners of war.

Her broadcasts recalled the earlier efforts of propagandists during World War II, known to American servicemen in the Pacific as Tokyo Rose and in Europe as Axis Sally. The United States, for its part, had sought to dampen the resolve of Hitler’s troops with recordings of Marlene Dietrich, the glamorous German-born Hollywood star, singing songs such as the melancholy war ballad “Lili Marlene.”

“This is Thu Huong calling American servicemen in South Vietnam,” Ms. Ngo would proclaim, using a name that she had selected for herself and that meant “Autumn Fragrance.” She did not learn until later that her listeners had dubbed her “Hanoi Hannah.”

“American soldiers liked word games,” she recalled. “I didn’t care what American soldiers called me. What mattered was that they listened to our radio programs for which they were the target audience.”

The broadcasts initially lasted five minutes but grew to run for a half-hour and included popular recordings from American musicians such as Elvis Presley and Bob Dylan. Having enticed homesick troops with music, Ms. Ngo would read scripts, prepared by North Vietnamese officials, that chronicled American battlefield defeats, as well as antiwar activity and social upheaval at home.

“Defect, G.I. It is a very good idea to leave a sinking ship,” she said in one broadcast. “You know you cannot win this war.”

She aired statements from actress and antiwar activist Jane Fonda and delivered commentary on the sons of elite American families who had avoided wartime service. Relying on information from U.S. publications, Ms. Ngo also read aloud lists of American casualties. The objective, she said, was to make the troops “a little bit sad.”

“Presenting news should be persuasive, not too intimate and not too tough,” she said. “When mentioning the war’s developments, I often quoted American newspapers to make the information more objective. The message that I wanted to send to each American soldier is, ‘You are fighting for an unjust war and will die in vain.’ ”

American forces withdrew from Vietnam in 1973, and Saigon, the southern capital later renamed Ho Chi Minh City, fell to the North Vietnamese two years later. Ms. Ngo said she was the announcer who reported on Voice of Vietnam that the city had been “liberated.”

She was reportedly married to an electrical engineer and had two children who were evacuated to the countryside during the war. When the war ended, the family moved south, where Ms. Ngo became a television broadcaster in Ho Chi Minh City. A complete list of survivors was not immediately available.

Ms. Ngo’s role in the outcome of the war, if she played any at all, was unclear. Some accounts of her work described her voice as “silky.” But a reporter for the Chicago Daily News in 1967 observed that she sounded “more like a nagging, whining wife than the sultry, beguiling female she tries to be.”

Among the servicemen who heard her broadcasts was John McCain, the Navy officer and future Republican senator from Arizona who was held by the North Vietnamese as a prisoner of war for 5½ years.

“I heard her every day,” McCain told the New York Times in 2000, recalling the loudspeaker that dangled from the prison ceiling. “She’s a marvelous entertainer. I’m surprised she didn’t get to Hollywood.”